1. Field of the Invention
This invention relates to Voice over Internet Protocol (VoIP) calls and more particularly to rerouting VoIP calls when quality of service degrades on an IP private network.
2. Brief Description of the Prior Art
Direct Inward Dialing (DID) is a service offered by telephone companies wherein customers pay for a single DID number (or block of numbers) and callers dial directly to an extension(s) on a Private Branch Exchange (PBX) or via a gateway, packet voice system, such as an IP private network. An ISDN DID trunk forwards the entire incoming called phone number (or a subset of the number) to the PBX or router/gateway. For example, a company may have assigned phones extensions 555-7000 to 555-7999. With a caller dialing 555-7234, the DID trunk might forward 234 to the PBX or, via gateway, packet voice system. The PBX or packet voice system rings extension 234 transparent to the caller.
In what is known as a Voice Over Internet Protocol (VoIP) call, an input audio stream (analog or digital) is quantized into digital packets. These digital packets are converted via a gateway to an Internet Protocol (IP) network and routed to a destination. Upon receipt of the VoIP packets, the destination decodes the digital packets, converting them back into a continuous digital audio output stream that is nearly identical to the input audio stream. The IP network may be a public network or a private network, e.g., behind a DID public access trunk. An IP private network is a network, wherein users communicate across a secure private Internet Protocol (IP) backbone, utilizing Asynchronous Transfer Mode (ATM) and/or frame relay connections, for example, to build IP-based intranets and extranets. It is highly scalable and reliable and may support Web based applications and content hosting.
The Quality of Service (QoS) of VoIP calls can degrade due to network congestion or network processing node failure. Degraded QoS can include anything from unintelligible calls to reduced ability and unresponsiveness of the IP private network in establishing new VoIP calls. Normally, VoIP survivability (i.e., network fallback) can only be initiated in the network layer (layer 3) of the International Organization for Standardization (ISO) standard model. This is true for most public and private networks, whether a local area network (LAN), a wide area network (WAN), or a Public Services Telephone Network (PSTN) e.g., Primary Rate Interface or PRI. When such an IP network is congested or breaks, whether communicating over a LAN or using ATM, network outages occur. Communications are lost during these outages unless calls are routed over another, alternate network e.g., PSTN.
Although, IP private network reliability may exceed IP public network reliability, VoIP still is not in the same class as a traditional switched PSTN. Consequently, it frequently may be necessary to place calls intended as VoIP calls back out on a traditional circuit switched network, especially when QoS is severely degraded. However, Integrated Services Digital Network (ISDN) or Basic Rate Interface (BRI) public protocols do not provide a mechanism in layer 3 to facilitate survivability or to correlate a hairpinned call (e.g., from/to another network) routed over the public network. Further, analog and non-ISDN digital PSTN trunks do not provide layer 3 services at all.
Normally, once a VoIP call is active, there is no way to then reroute the call through a PSTN and then synchronize the voice call with the VoIP call, especially for calls made behind a DID trunk and over a IP private network. Thus, if QoS of the IP private network degrades during a VoIP call, the quality of the remainder of that VoIP call will be degraded. By contrast, if a problem is detected before a new VoIP call is established, the entire call may be alternately routed over the PSTN network. However, even if communication over the IP private network improves to an acceptable quality level, the remainder of that call continues over the PSTN.
Hairpinning is even more difficult on an IP private network behind a DID trunk. Re-routing IP traffic when the network fails, is a known deficiency of IP networks, normally requiring an expensive duplicated/redundant network. For example, to use a public network as an alternate network, the private network user must know to dial out to a public number rather than a private extension number to reach an in-network destination. When the call connects, the party being called receives the call unaware that the incoming call is a private network call because it looks like a normal public call. Also, none of the private network features are passed along to the called party when the call is alternately routed over the public network. Only users with a public DID number can receive alternate routed PSTN calls addressed or directed to them. Because of the expense for each DID number, many private network users do not get their own public number. Instead, they have a private extension number and incoming public trunks can only be transferred to them or, they may be in a hunt group.
In addition, IP Private network users must be aware of which network (private or public) they are using in order to send and receive calls correctly. Otherwise, alternately routed calls must be initiated by network administration. Network addressing may differ for these alternately routed calls, and normal network features may be different or non-existent. As a result the called party experiences operational differences, e.g., loss of caller identifiability. Finally, VoIP private network users that do not have a DID number would be unreachable during periods of extreme QoS degradation or network failures. So, it is important to provide high quality calls overs an IP private network.
Thus, there is a need for private networks and methods that seamlessly switch VoIP calls to alternate networks as needed when communications degrade.